1. Field of the Invention
The invention relates to a dual key bi-step lock, and more particularly, to a lock having a primary key and a secondary key which is able to be used as a universal key or an emergent key.
2. Description of Related Art
A conventional pin tumbler lock usually has a shell having formed therein a central cylindrical opening in which is located a plug. The shell further has formed therein a set of chambers, each of which is a radially extending bore adapted to receive therein a pin stack which includes a compression spring, a driver pin, and a key pin. The key pin is outermost, and is supported on the driver pin, which is seated in turn on the compression spring, which assists in forcing the key pin across a shear line and into the keyway formed in the plug, so as to block rotation thereof within the cylinder. In this position, the lock cannot be opened without a key. The driver pins are of uniform length, while the key pins are of different lengths.
Chinese patent ZL93243828.8 discloses a pin tumbler lock having a universal key. For one batch of this kind of lock, the universal key is able to open all the locks but the special key is only able to open one special matching lock. For this kind of lock, either the universal key or the special key will be able to open one special lock individually. It is desired that a lock is only able to be opened when the universal key and the special key are both inserted in a keyway of the lock.